The present invention relates to a resin coating pipe mostly used in a fuel filler pipe of an automobile or the like, and a manufacturing method thereof.
FIG. 7 is an perspective view showing a fuel tank and a fuel filler pipe of an automobile. The fuel tank 1 is located at a lower portion of a body of an automobile, and the fuel filler pipe 2 is installed so as to connect the fuel feed portion 3 provided at the body outside plate and the fuel tank 1. In the course of the fuel filler pipe 2, an elastic pipe 4 formed from an elastic material such as a rubber is connected, and by the elasticity of this elastic pipe 4, the error (difference) in the relative position of the fuel feed portion 3 and the fuel tank 1 or the vibration are arranged to be absorbed.
As a material of the fuel filler pipe 2, a material which is excellent in corrosion resistance such as a stainless pipe is preferable, but a stainless pipe is expensive and further, it is scarce of processability such as bending workability, and therefore, commonly, a pipe material made by performing surface treatment such as plating or cationic electro-deposition coating onto the surface of a steel pipe which is cheap and has a good workability, is used as a material of the fuel filler pipe 2. The steel pipe material like this is used such that after it has been subjected to bending processing or the like, a resin coating layer such as a layer of polyethylene is further formed on the surface thereof, and it is made to be a resin coating pipe so that the corrosion resistance thereof may greatly be raised.
As a forming method of a resin coating layer in a resin coating pipe like this, for example, there is such a method that after electrostatically attaching a powdered resin material onto the surface of a pipe material, the pipe material is heated so that the resin material may be melted to form the resin coating layer, or there is such a method that a powdered resin material is sprinkled and attached to a previously heated pipe material, and after that, further, the pipe material is heated to form a resin coating layer.
However, in any above mentioned method, the thickness of the resin coating film is thick (not less than 0.3 mm), and if this thick resin coating layer is applied even to the end potion of the fuel filler pipe 2, the insertion into the elastic pipe 4 becomes difficult, and therefore, it is necessary to mask the peripheral surface near the end portion of the fuel filler pipe 2 through a specified length so that the resin coating layer may not be formed.
Previously, it has been arranged that first, as shown in FIG. 8, the masking member 5 formed approximately in a cylindrical shape (like a cup) from a material such as a heat resistant rubber, is fitted onto the end portion of the pipe material 6, and next, as shown in FIG. 9, a powdered resin material is attached to the rest part of the surface of the pipe material 6 and is subjected to heat treatment to form a resin coating layer 7, and finally, the masking member 5 is removed to complete the fuel filler pipe 2, and as shown in FIG. 7 and FIGS. 9, 10, the portion which has been masked is inserted into the inside diameter portion of the elastic pipe 4 as an insertion portion 8.
However, after the insertion portion 8 of the fuel filler pipe 2 has been inserted into the inside diameter portion of the elastic pipe 4, it often occurs that the elastic pipe 4 is a little shifted in the direction of slipping off from the insertion portion 8 under the influence of the contraction phenomenon of the elastic pipe 4 itself, the running vibration of the vehicle, or the like, and consequently, as shown in FIG. 10, between the end portion of the resin coating layer 7 and the elastic pipe 4, a clearance C is produced. At this portion of the clearance C, the insertion portion 8 where the resin coating layer 7 is not formed (skin of the pipe material 6) is exposed to the outside, and further, water can easily enter into the clearance C, and consequently, the possibility that the fuel filler pipe 2 may suffer corrosion from the portion of the clearance C, has been high.